install does nothing if you delete elm-stuff/packages but leave exact-dependencies.json

[thewoolleyman]

I can provide an SSCCE if desired, but the subject should be self explanatory.

This is related to, and a prerequisite for, https://github.com/elm-lang/elm-package/issues/217

The context of this issue is the overall goal of being able to commit exact-dependencies.json to source control, so it has a preserved, revertable history of all changes to it. I ran into this issue in my first attempts to use Elm, because I'm in the habit of always committing the full dependency graph of my projects to source control (e.g. Gemfile.lock, npm-shrinkwrap.json).

Here's simple steps to reproduce:

1. Adding only elm-stuff/packages and elm-stuff/build-artifacts to .gitignore (thus allowing elm-stuff/exact-dependencies.json to be committed)
2. Cause elm-stuff/packages to be deleted (e.g. via git clean -df)
3. All subsequent invocations of elm-package install will do nothing (i.e. leave the packages dir empty).
4. This then causes subsequent attempt to build the project with elm-make to fail with an error like this (obviously, because the core packages do not exist):

elm-make: elm-stuff/packages/elm-lang/core/5.0.0/elm-package.json: openBinaryFile: does not exist (No such file or directory)

In looking at the source code briefly, I think I see the problem.

It's because the existence of an exact-dependencies.json in Install.hs is assumed to imply that the required packages do not need to be installed, based on a simple diff of old and new in Plan.hs.

The simple solution seems to be to make the Plan check for the actual existence of all of the required packages' files, and force a re-install of them if they are missing.

[eeue56]

Fixed by https://github.com/elm-lang/elm-package/pull/246

[thewoolleyman]

@eeue56 Hi, thanks for the comment and reference. Unfortunately, I don't think #246 fixes this specific issue. It recreates the directory if it's missing, but doesn't cause elm-package install to reinstall missing packages which may have been deleted.

I built from the latest source on master, and was still able to reproduce the problem:

# using fix from #246:
○ → cat /Users/woolley/workspace/elm-package/src/Install.hs | grep 'ensure we have the stuff directory'
      -- ensure we have the stuff directory before doing anything else

○ → /Users/woolley/workspace/elm-package/dist/build/elm-package/elm-package
elm-package 0.18.0

# remove packages dir:
○ → rm -rf elm-stuff/packages/

# get same message as before:
○ → /Users/woolley/workspace/elm-package/dist/build/elm-package/elm-package install
Packages configured successfully!

# yet nothing was installed, as before:
○ → ls elm-stuff/packages

# and problem still, obviously, occurs because no packages exist:
○ → elm-make Hello.elm
elm-make: elm-stuff/packages/elm-lang/core/5.0.0/elm-package.json: openBinaryFile: does not exist (No such file or directory)

[evancz]

In 0.19 an application will have all of the exact dependencies listed in the elm.json file, so there will be no separate exact-dependencies.json file that you must check in and treat as a lock file.

The intent of elm-stuff/ is that it is managed entirely by Elm, so messing with it is basically corrupting that state. By moving the "lock file" information into elm.json I believe there will be no reason to partially delete elm-stuff/, thereby resolving the root issue here.

Based on that understanding, I will close.